The Fortitude Gold Skarn Deposit

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Gold skarns have total gold production/reserves about four times greater than U.S. annual mine production and are the focus of major exploration programs on several continents, yet little is known about their geology, mineralogy, geochemistry, or petrogenesis. The proposed research will document the stratigraphic setting, petrology, mineralogy, fluid inclusion characteristics, trace element geochemistry, and stable isotope signature of the largest and most economically important gold skarn in the world. The basic approach for the study will be detailed geologic mapping. The importance of a clastic rich, carbonaceous, carbonate sequence may play a key role in the evolution of the hydrothermal system, buffering subsequent calc-silicate and sulfide mineral assemblages. These reducing conditions are reflected in the ferrous iron dominant calc-silicate assemblages and reduced sulfide species. Preliminary work indicates that pyroxenes from many gold-bearing skarn systems tend to be more iron-rich (up to pure hedenbergite) and amphiboles and garnets t end to be more aluminum-rich, than most other skarn types. One of the goals of this study is to establish a genetic model for the evolution of the Fortitude gold skarn deposit; in particular, to answer the questions, "What is a gold skarn?" "How does one form?", and "What exploration criteria can be used for their discovery?" At present these important scientific and economic questions cannot be answered. The research outlined in this proposal is designed to find the answers using the most important and well exposed system.